The present invention relates generally to surgical devices for the repair of split portions of tissue, in particular, to surgical devices for closing a severed sternum.
The sternum is an elongated, flattened bone, forming the middle portion of the anterior wall of the thorax. Its upper end supports the clavicles, and its margins articulate with the cartilages of the first seven pairs of ribs. It consists of three parts, named from the neck downward, the manubrium, the body, and the xiphoid process. Its average length in an adult is about 17 cm, and is slightly less in a female adult. The sternum is a composite bone structure with a thin cortical shell surrounding a low-density cancellous core. Cortical bone is ivory-like and is dense in texture without cavities. It is the shell of many bones, surrounding the cancellous bone in the center. Cancellous bone is sponge-like with numerous cavities.
During surgery involving thoracic organs such as the heart, lungs, esophagus and aorta, it may be required to split the sternum to provide sufficient access for the surgeon. A partial or median sternotomy is a procedure by which a saw or other cutting instrument is used to make a midline, longitudinal incision along a portion of, or the entire axial length of the patient's sternum, allowing two opposing sternal halves to be separated laterally. Upon completion of the surgery, the sternum is rejoined and closed.
The two sternal halves are typically closed with stainless steel wire sutures that engage the severed sternal edges in a face-to-face relationship and compress them together while the sternum heals. The wire sutures are wrapped around the sternal halves by passing them through the intercostal spaces adjacent to the sternum. They may also be pierced through both halves of the sternum, particularly near the manubrium. Various piercing and wrapping patterns are used by different surgeons. For example, the wire sutures may be applied in an “X” pattern as viewed from the anterior portion of the sternum, to reduce axial motion of the sternal halves relative to each other. Regardless of the method, the ends of the wire sutures are twisted together to tighten the wire loops to a point where the sternal edges are approximated under tension.
U.S. Pat. No. 3,802,438 discloses sternal closure with wire sutures in conjunction with a splice plate in which the wire sutures are received. Other sternal closure assemblies include one or two metal plates, these plates being provided with rows of openings, through which extend the screws, pins, or metal wire, to bring together the severed portions of the sternum. In U.S. Pat. No. 4,583,541, wire bands are used in concert with an elongated, generally strap-like board, placed at the front of the sternum through which the wires are passed. Knots are then made and the knots then placed within a groove in the board.
Clamps, clasps, bands, and strips have been developed as sternal closure devices. For example, U.S. Pat. No. 4,201,215 discloses the use of a two-piece C-shaped clamp at one side of the sternum, the clamp pieces having hook ends that pass around to the other side of the sternum. Other assemblies completely circle the sternum and employ complex locking mechanisms to effect compression of the two sternal halves together. Representative examples are described in U.S. Pat. Nos. 5,356,417; 5,462,542; and 6,007,538.
There are numerous drawbacks with the use of wire sutures. For example, surgeons typically do not have means for ensuring that the tension in one wire suture is the same as the tension in another. Another drawback is that excessive twisting of the wire suture during tensioning can also result in hardening of the wire suture and breakage during the sternal closure procedure or after the surgical procedure. After being twisted together, the excess wire suture must be cut away, leaving sharp ends which may be palpable through the skin, painful and cosmetically undesirable. Surgeons may also be concerned about the potential for the wire suture to injure small blood vessels or nerves near the underside of the sternum. Moreover, the use of devices such as clamps, etc., that completely wrap around the sternum may irritate or damage tissue and vital structures such as blood vessels, particularly on the underside of the sternum.
Another drawback with the use of wire suture is that the amount of force necessary to close the sternum may cause the wire suture, which has a very small load-bearing surface, to cut through the cortical and cancellous portions of sternum. Additionally, the wire suture may cut through the cortical and cancellous portions of the sternum after sternal closure has been achieved, particularly when the wire sutures are subjected to intermittent severe loading due to coughing and other movements of the patient. These loads are transmitted primarily through the wire suture to the cortical component of the sternum. In some cases, this results in a loosening of a wrapped wire suture or an enlargement of the pierced holes in the sternum when the wire suture is pierced through the sternal halves. This loosening of the wrapped wire suture or the enlargement of the holes enables motion of the two halves of the sternum relative to each other. This motion may allow the sternal halves to separate and inhibit proper wound healing. In some cases, this separation may further allow opportunistic organisms to invade the tissue and cause an infection. Such an infection in the sternum is associated with significant morbidity and sometimes death. None of the devices described above that utilize wire sutures offers protection from shear loading and the resultant axial motion of the sternal halves.
Ideally, the device chosen to close a severed sternum must be simple in design, safe and easy to implant and remove, and should not damage adjacent tissue. It should not cause irritation to the patient or be cosmetically unacceptable. It must also be able to provide a secure sternal closure when challenged with post-surgical movement by the patient, particularly coughing. It is therefore an object of the present invention to provide a device and method that overcome the disadvantages of those known in the art.